This invention relates generally to the rotor windings of a dynamoelectric machine, and particularly, to means for ventilating the end turn windings.
The rotors, in large gas cooled dynamoelectric machines, have a central rotor body portion defining a plurality of axial winding slots within which are disposed a plurality of rotor windings. The slots are circumferentially spaced on the periphery of the rotor body on either side of a pole portion.
To generate the electromagnetic field for the dynamelectric machine, a number of conductors carry current in loops about each pole of the rotor. The conductors are radially stacked in groups with interposed layers of insulation between each conductor in a particular group. As is well recognized in the art, the intensity of the field is related to the level of voltage applied to the conductors which form the rotor winding and the amount of current flowing through the conductor. It is sometimes desirable to utilize higher voltages and proportionally lower currents for dynamoelectric machines. However, the higher voltages, and lower currents require that more turns or conductors be placed in the same winding slot.
This requirement for more turns per winding slot translates into a requirement that each conductor in the slot must be thinner if the rotor's size is constant. It is commonly recognized that the conductors utilized in the above-mentioned rotors are copper bars, although other highly-conductive metals such as aluminum and silver are sometimes utilized as conductors.
Another important consideration relates to the cooling of the windings in the rotor. It is well recognized in the art, that heat is generated in the conductor due to the currents flowing through the windings. To remedy this situation, the axially extending portions of the conductors disposed in the winding slots (hereinafter termed "slot-lying conductors"), are cooled by gas flowing through a plurality of gas cooling channels. Other means of cooling utilize substantially diagonal channels in each group of conductors in communication with intake flues at the pole face, and with the periphery of the rotor body. A more complete description of a cooling means appears in U.S. Pat. No. 2,986,664, issued to Willyoung et al. which describes a diagonal flow, direct cooled rotor and that description is incorporated herein by reference thereto. It is recognized that if the slot-lying conductors must be cooled due to I.sup.2 R heating problems, the end turn conductors must also be cooled.
The end turn conductors include the axial extensions of the slot-lying conductors and a plurality of circumferential end turn conductor members which complete the current carrying loops of the rotor winding. The axial end turn conductors are the axial extensions of the slot-lying conductors extending beyond the rotor body. Although a distinction is made herein between the slot-lying conductors and the axial end turn conductors, both of these conductors are in fact one continuous axially extending conductor. Each circumferential conductor is mechanically and electrically connected to a corresponding axial end turn conductor, hence both conductors are stacked, either circumferentially or radially, with interposed layers of turn insulation therebetween. A retaining ring is affixed to the rotor body and circumferentially surrounds and holds the end turn conductors in place against circumferential force, such as centrifugal force developed during rotation of the rotor. A centering ring is affixed to the retaining ring and is axially spaced from the rotor body to substanially enclose the end turn conductors in cooperation with the retaining ring and the rotor body. Spindles extend from either axial end of the rotor body. In this manner, an end turn region is defined by the rotor body, the radially inner portion of the retaining ring, the surface of the spindle and the inboard surface of the centering ring.
Cooling of the end turn conductors has been accomplished by prior art devices in many ways. One well known mechanism utilizes two bars of copper for each conductor. The bars have longitudinal grooves facing each other and the bars are stacked upon each other to form a passage through each conductor. This two bar configuration allows gas flowing through the passage formed by the two facing grooves to cool the conductor.
It is well recognized in the art that cool gas, proximate to the centering ring and spindle, is drawn into the end turn region through an annular space defined by the radially inward portion of the retaining ring and the radially aligned surface portion of the spindle due at least in part to the centrifugal pumping action. This centrifugal pumping action is caused by the rotation of the rotor and the radial differential between the gas intake and the gas exhaust, i.e., the annular space and the periphery of the rotor body. As is well recognized in the art, the rotor body, and sometimes the slot-lying conductors, form gas discharge flues which open to the periphery of the rotor body.
One prior art device, described in U.S. Pat. No. 3,005,119, issued to Schmitt et al., shows a series of supports to hold the end turn conductors, and a series of baffles sectioning off the end turn region to create a plurality of high and low pressure sections in that region. A series of passages in each axial end turn conductor and circumferential end turn conductor provide means for cooling gas to flow throuh those conductors. The device disclosed in Schmitt et al. utilizes a two bar conductor scheme with each bar hav a groove or hollow extruded section which faces a similar groove or extruded section of the other bar. Also, the apparatus disclosed in Schmitt et al. is complicated to manufacture because of the number of baffles separating the high and low pressure sections. The above-noted patent issued to Schmitt et al. is incorporated herein by reference thereto.
Another prior art device disclosed in U.S. Pat. No. 3,225,231, issued to Kudlacik, utilizes a set of baffles defining high and low pressure sections in the end turn region. Also, the Kudlacik device includes a plurality of radially cutouts through the centering ring which act as radial passages to discharge the gas from the low pressure areas to the periphery of the retaining ring. Again, the conductors are twin bars having longitudinally extending internal gas cooling passages which open onto the high and low pressure sections. The patent issued to Kudlacik is incorporated herein by reference thereto.
Although it is known to construct rotor windings utilizing single bars for the axially extending conductors, problems have arisen regarding end turn ventilation of the portions of those single, integral bars axially extending beyond the rotor body. Cooling the slot-lying portion of those integral bar conductors can be accomplished by known mechanisms. Cooling the end turns of those single bar conductors is difficult because the physical connection between the axial end turn conductors and the circumferential end turn conductors must be strong.
Typically, the corner includes a reinforcing plate with a gusset to strengthen the connection. The gusset is on the inboard portion of the plate. The gusset is preferably spaced from the underlying and overlaying stacked conductors, hence the gusset is recessed from the conductor's top and bottom surfaces. This spacing is preferable because the interposed layer of turn insulation is not easily extended to cover the gusset.
Generally, prior art devices utilizing a twin bar conductor system had six to twelve turns per winding slot, or six to twelve conductors per slot. To increase the number of turns, it is desirable to have single bar conductors, however the prior art devices for cooling the end turn conductors do not address single bar axial conductors. One of ordinary skill in the art will recognize that relatively thin twin bar conductors, those conductors being less than one-half of an inch, are not easily manufactured with facing grooves forming cooling passages. Similarly, a single, integral conductor bar due to the difficulty in manufacturing those passages is not easily manufactured with a completely internal cooling passage therein. A person skilled in the art will recognize an end turn ventilation scheme utilizing those relatively thin integral bars would be highly desirable because the number of turns in the field winding could be increased simply by making the bars thinner given a rotor of a certain radial dimension. Another complication of the single bar conductor system involves connecting the axial end turn conductors to the circumferential end turn conductors.